package com.base.common.util.algorithm;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;



public class Base64 {
  private static final char[] legalChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();

	/**
	 * data[]进行编码
	 *
	 * @param data
	 * @return
	 */
      public static String encode(byte[] data) {
          int start = 0;
          int len = data.length;
          StringBuffer buf = new StringBuffer(data.length * 3 / 2);

          int end = len - 3;
          int i = start;
          int n = 0;

          while (i <= end) {
              int d = ((((int) data[i]) & 0x0ff) << 16)
                      | ((((int) data[i + 1]) & 0x0ff) << 8)
                      | (((int) data[i + 2]) & 0x0ff);

              buf.append(legalChars[(d >> 18) & 63]);
              buf.append(legalChars[(d >> 12) & 63]);
              buf.append(legalChars[(d >> 6) & 63]);
              buf.append(legalChars[d & 63]);

              i += 3;

              if (n++ >= 14) {
                  n = 0;
                  buf.append(" ");
              }
          }

          if (i == start + len - 2) {
              int d = ((((int) data[i]) & 0x0ff) << 16)
                      | ((((int) data[i + 1]) & 255) << 8);

              buf.append(legalChars[(d >> 18) & 63]);
              buf.append(legalChars[(d >> 12) & 63]);
              buf.append(legalChars[(d >> 6) & 63]);
              buf.append("=");
          } else if (i == start + len - 1) {
              int d = (((int) data[i]) & 0x0ff) << 16;

              buf.append(legalChars[(d >> 18) & 63]);
              buf.append(legalChars[(d >> 12) & 63]);
              buf.append("==");
          }

          return buf.toString();
      }

      private static int decode(char c) {
          if (c >= 'A' && c <= 'Z')
              return ((int) c) - 65;
          else if (c >= 'a' && c <= 'z')
              return ((int) c) - 97 + 26;
          else if (c >= '0' && c <= '9')
              return ((int) c) - 48 + 26 + 26;
          else
              switch (c) {
              case '+':
                  return 62;
              case '/':
                  return 63;
              case '=':
                  return 0;
              default:
                  throw new RuntimeException("unexpected code: " + c);
              }
      }

      /**
       * Decodes the given Base64 encoded String to a new byte array. The byte
       * array holding the decoded data is returned.
       */

      public static byte[] decode(String s) {

          ByteArrayOutputStream bos = new ByteArrayOutputStream();
          try {
              decode(s, bos);
          } catch (IOException e) {
              throw new RuntimeException();
          }
          byte[] decodedBytes = bos.toByteArray();
          try {
              bos.close();
              bos = null;
          } catch (IOException ex) {
              System.err.println("Error while decoding BASE64: " + ex.toString());
          }
          return decodedBytes;
      }

      private static void decode(String s, OutputStream os) throws IOException {
          int i = 0;

          int len = s.length();

          while (true) {
              while (i < len && s.charAt(i) <= ' ')
                  i++;

              if (i == len)
                  break;

              int tri = (decode(s.charAt(i)) << 18)
                      + (decode(s.charAt(i + 1)) << 12)
                      + (decode(s.charAt(i + 2)) << 6)
                      + (decode(s.charAt(i + 3)));

              os.write((tri >> 16) & 255);
              if (s.charAt(i + 2) == '=')
                  break;
              os.write((tri >> 8) & 255);
              if (s.charAt(i + 3) == '=')
                  break;
              os.write(tri & 255);

              i += 4;
          }
      }

}
